Th antibiotic 1-carba-2-penem-3-carboxylic acid is reported by Cama and Christensen in JACS, 100, 8006 (1978). 1-Carba-2-penem-3-carboxylic acid is prepared chemically, and prior to this invention, has not been found in nature.
1-Carba-2-penem-3-carboxylic acid, p-nitro-benzyl ester can be prepared from the corresponding free acid and can be used to prepare various 2-substituted-1-carba-2-penem-3-carboxylic acids which have antibacterial activity; see Basker, et al., J. Antibiotics, 34:1224 (1981).